How Can I Tell If My Pepper Plants Need Iron?

Healthy pepper plants have dark green leaves.

Iron is one of the essential elements for photosynthesis. Without it, pepper (Capsicum spp.) plants lose their bright green color and fail to thrive. Iron-deficient pepper plants show an easily recognized color pattern on the leaves. The color pattern tells you that the plant needs iron, but it doesn't tell you whether the iron deficiency is due to lack of iron in the soil or low soil pH, which prevents plants from absorbing available iron.

Symptoms of Iron Chlorosis

Chlorosis means yellowing of the leaves. You can tell iron chlorosis from yellowing caused by other problems because the leaves of the pepper plants turn yellow between the veins, but the veins themselves remain green. Chlorosis due to iron deficiency begins on young leaves. In severe cases the leaves might also develop scorched edges and angular brown spots. The yellow color is reversible, and pepper plants recover once you correct the problem.

Soil pH and Iron Deficiency

High pH can reduce a pepper plant's ability to absorb iron by making the iron in the soil less soluble. This is especially true of sandy or desert soils with a pH above 8.0. A high soil pH doesn't rule out the soil being deficient in iron, but you may find that you only need to treat the pH problem to correct iron chlorosis. A soil test will give you the definitive answer about the cause of iron deficiency. It is very difficult if not impossible to acidify soil that is high in calcium carbonate or caliche, and in these cases it's best to grow peppers in containers.

Acidifying the Soil

Pepper plants grow best in a soil with a pH between 6.5 and 7.5. If the pH is above 7.5, the plants might not be able to absorb iron and other nutrients. Apply elemental sulfur to the soil at the rate of 1/2 to 1 pound per 100 square feet of planting area to correct the pH. Test the soil again after three months and repeat the treatment, if necessary. Peat or sphagnum peat moss also help to adjust the soil pH, and soils with higher organic content maintain the pH adjustment longer.

Correcting Iron Deficiency

Correct iron deficiencies with iron fertilizers labeled as chelated iron. Work 3 to 5 ounces of fertilizer into each 100 square feet of soil and watch for improvement in leaf color and vigor. You will probably have to repeat the treatment several times over the growing season to correct the problem.

About the Author

Jackie Carroll has been a freelance writer since 1995. Her home-and-garden and nature articles have appeared in "Birds & Blooms" and "Alamance Today." She holds a Bachelor of Science in medical technology from the University of North Carolina.